Prior art surgical procedures on the spine are substantially invasive. Even procedures currently marketed as “minimally-invasive” typically require incisions that are several inches long. Because smaller incisions and less invasive procedures would result in shorter hospitalizations and faster patient recovery, a procedure that is truly minimally invasive (or “micro-invasive”) is desirable. It is estimated that using the equipment and procedures set forth herein could shorten typical post-operative hospital stays from three to five days to one day for spinal stabilization and spinal fusion procedures.
Nevertheless, the prior art minimally-invasive spinal procedures have increased in popularity over the course of the past decade. Compared to the open techniques that came before them, these prior art minimally-invasive procedures allow patients to experience shorter hospital stays, faster post-operative recoveries, and an earlier return to work. These procedures were initially limited to simple decompressive procedures. Over the past few years, however, surgeons have begun to expand the applications of these systems to include spinal stabilization and spinal fusion procedures.
FIG. 1 shows two generic vertebrae 100, and FIG. 2 shows a top view of FIG. 1. The front (or “anterior”) portion of the vertebra 100 is the body 102. The bodies 102 of adjacent vertebrae 100 are typically separated by an intervertebral disk 154. Posteriorly, the body 102 is joined by a left pedicle 104 and right pedicle 106 to the lamina 108. The lamina 108 joins a spinous process 114 that generally serves for muscle and ligamentous attachments. Transverse processes 110 and 112 project laterally from the junction of the respective pedicle 104, 106 and the lamina 108 and also serve for muscle and ligamentous attachments. A supraspinous ligament attaches the spinous processes 114 of adjacent vertebrae 100 to provide stability to the spinal column.
The lamina 108, pedicles 104, 106, and body 102 surround a passageway known as the vertebral foramen 116. The vertebra 100 also has articular processes 118 that extend above and below the vertebra 100 to interact with adjacent vertebra 100; these interactions are known as facet joints.
While the parts of vertebrae 100 shown in FIG. 1 and FIG. 2 are common to most vertebrae 100 of the spinal column, details of anatomy differ with position of the vertebra 100 in the spinal column. For example, the vertebral body 102 is wider at lower levels of the spinal column, such as the lumbar region, than in vertebrae of the cervical spine; this provides greater weight-bearing capability at the lower levels. The body 102 of each vertebra is located anterior to the lamina 108 and spinous process 114. The spinal cord—or for lumbar vertebrae 100 its caudal extension, the cauda equina—passes through the vertebral foramen 116. Also found within the vertebral foramen 116 exiting the spinal cord are dorsal and ventral roots, arteries, veins, and a posterior longitudinal ligament 120 that attaches each vertebra 100 to its adjacent vertebrae 100. In addition, there is an anterior longitudinal ligament 122 that attaches each vertebra 100 to its adjacent vertebrae 100. Motor and sensory nerves exit the spinal canal together at a space between pedicles 106, 104 of adjacent vertebrae 100 known as intervertebral or neural foramina.
As a subject ages, or suffers injury, various disease processes may narrow, or impinge on, the spinal canal defined by successive vertebral foramens 116 such that less space is available for the spinal cord, nerve roots, and other tissues. Among these disease processes may be bulging or rupture of an intervertebral disk 154 that impinges on the spinal canal, tumors, abscesses, ligamentous hypertrophy, spondylolisthesis, ossification of the posterior longitudinal ligament, bone spur formation, etc. Whenever the spinal canal, defined by successive vertebral foramina 116, is effectively narrowed by a disease process impinging on the spinal cord, cauda equina, or nerve root, function may be impaired. This may result in symptoms of numbness, weakness, ataxia, impotence, incontinence, pain, and even paralysis. In some subjects, it is necessary to surgically decompress the neural elements to prevent further damage and provide relief of symptoms. Surgical decompression often requires a laminectomy to provide additional room for the spinal canal, which involves cutting through the lamina 108 on both sides of the spinous process 114 and subsequently removing this segment.
Further, damage to (including fractures) or diseases (including arthritis) of the vertebral body 102, the facet joints 118 between vertebrae 100, or the intervertebral disks 154 between adjacent vertebral bodies 102 may require surgical intervention. And in some patients, vertebral bodies 102 may be anteriorly displaced in relation to each other. This may result from fractures or diseases of the facet joints 118, or from defects in the pars interarticularis, and is known as spondylolisthesis.
A known surgical stabilization technique is spinal fusion with instrumentation; this has traditionally been done using an open surgical technique where the spinal column is approached from the front through the abdomen to gain access to the vertebral body 102, and/or from the back. In this surgery, an intervertebral disk 154 between two vertebrae 100 is often removed and replaced with an implant that is typically made of bone, metal, or another appropriate substance. This type of surgery is known as an interbody fusion. The implant provides the necessary matrix to allow bone growth and healing to fuse the adjacent vertebrae 100. Posterolateral fusions can also be performed between the transverse processes 110 and 112 of adjacent vertebrae. Other repairs to the vertebral body 102 may also be done.
After the matrix for fusion has been established (i.e. via posterolateral and/or interbody fusion), instrumentation is often utilized to stabilize the spinal column and promote fusion (arthrodesis) by preventing micromotion of the instrumented adjacent vertebra 100. Several different forms of instrumentation have been developed in the past. However, biomechanical studies have proven that pedicle screws provide the most effective form of lumbar spinal instrumentation with the highest pull-out strength. Pedicle screws are placed from a posterior approach at the junction of the transverse process 110, 112 and facet 118. These screws are then passed through the pedicle 104, 106 into the vertebral body 102. The pedicle screws of adjacent vertebral bodies 102 are then attached to rods, and this construct provides stabilization to the fused segment by preventing micromotion.
Conventional open surgical techniques typically utilize larger incisions, as direct visualization of the vertebral structures is required, and occasionally require both anterior and posterior approaches to the spine. Prior art minimally-invasive techniques, as noted above, typically utilize incisions that are several inches long, which results in hospitalizations and recoveries that are marginally better than comparable open surgical techniques. Micro-invasive systems and methods, such as those set forth herein, may result in shorter hospitalizations, faster post-operative recoveries, less narcotic dependence, and earlier return to work than both open and prior art minimally-invasive techniques.